Note: I couldn't decide whether to post this to society or to health, in the end I think it's more important that people interested in the protests see it, but feel free to move this.

I have not seen an LRAD from up close, I'm going from what is available online and my knowledge of acoustics. There's a lot of misinformation floating around that could be dangerous for protestors, so I'm trying to clear up the worst of it.

What are LRADs/sound cannons?

LRADs are incredibly loud highly directional loudspeakers capable of reproducing medium to high frequencies. They can be used for communication, but they can also be used for playing tones or alarms at volumes so high that it completely paralyzes a person even with ears covered or earplugs inserted. This mode can easily cause immediate permanent hearing damage.

This is what they look like (sorry for daily mail link, but it's a decent current article)

The police in Minneapolis did not use it as a weapon yet afaik, they only used it to amplify voice and threaten to actually use it, so hopefully there was no harm done unless someone was standing close to it. However I think that in current political climate we have to assume that this can change at any time.

Benn Jordan's video on LRADs is wrong

I have seen links to a video by Benn Jordan on LRADs posted again in various places. Ignore this video and warn anybody who posts it as it's completely wrong and you are going to get hearing damage if you listen to it. Benn Jordan did not do his research and is shockingly lacking some fundaments of acoustics, I could write a whole post on that, but let's focus on the most imporant thing:

The video is about ultrasonic modulation speakers, whereas afaik all of the common LRADs are "just" incredibly loud normal loudspeakers. Here's a teardown that makes it obvious, some evidence can be found on the manufacturer's website as well.

Which means that most of what he says in the video simply does not apply. Most importantly, a piece of stiff glossy paper or plastic foamboard, which people on reddit or youtube keep posting about, will not help at all, it will do nothing, and if you ever try to rely on it, you're going to get hearing damage!

What does help?

The only thing that truly does help is always keeping your distance from an LRAD and/or at least standing far enough from the angle in which it produces maximum volume, which is about 15°. I believe a relatively safe distance without any hearing protection would be about 200 meters (about 650 feet) for the loudest models, but even then it just gives you time to GTFO.

If you need to be closer, wear earplugs. Soft foam earplugs cost almost nothing and may prevent hearing damage (but not if you're close and the LRAD is used at maximum volume). Something like this will provide more isolation. If you expect to be close to an LRAD, wearing large over the ear protection, as strong as you can get, with earplugs underneath is a good idea. Even that won't shield you from 150+ dB, so do not ever get too close.

A stiff, large and heavy shield will help. There's a link at the bottom with more information. However this only shields direct sound, and sound reflects off things, so if you're near a wall, or in a narrow street, you may still get dangerous volume levels just from reflected sound. I think it's usually safer to stay mobile than to carry around a heavy shield.